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The Basic Principles of X-ray Fluorescence
2020 06 22

The Basic Principles of X-ray Fluorescence

X-ray is a special device used by the German physicist Rogentgen when studying the experiment of rare gas discharge, this device emits electrons, a metal anode is placed at a position opposite the cathode, and a high voltage is applied between the anode and cathode. When the container is filled with a thin gas, the discharge phenomenon can be observed in the gas. The unknown ray found the experiment, Roentgen named X-ray. X-ray is defined as: the electromagnetic radiation emitted when electrons are accelerated near the nucleus or a transition occurs between outer nuclear energy levels

When the container is filled with a thin gas, the discharge phenomenon can be observed in the gas. The unknown ray found in the experiment, Roentgen named X-ray. X-rays are defined as: electromagnetic radiation emitted when electrons are accelerated near the nucleus or when transitions occur between the outer nuclear electron levels. X-ray fluerscence is secondary X-rays generated when primary X-rays irradiate the sample to be tested, the incident X-ray has a relatively large energy, making it possible to bombad electrons located in the inner layer of element atoms. The wavelength of the X-ray fluorescence spectrum is between 0.01-10nm,and the energy is between 124KeV-0.124KeV. The wavelength range of X-ray fluorescence spectrum used in elemental analysis is between 0.01-11nm, and the energy is 0.111-0.124KeV.

 

When the characteristic X-rays of the samples are excited by X-rays, the incident electromagnetic radiation energy must be greater than a certain value to cause the inner electronic excited state to form holes and cause electron transitions, this value is the absorption limit, equivalent to the work function of the inner electron, if the energy of the incident electromagnetic radiation is lower than the absorption limit, under no circumatances can the atomic inner electrons be excited and produce characteristic X-rays.

X-ray Excitation

Elements are composed of atoms, each atom has the same chemical properties, and atoms are composed of nucleus and extranuclear electrons. The extranuclear electrons are distributed according to the layered rule, thus forming the electron shell structure of the atom, the electron shell is divided into multiple layers from inside to outside, each shell can hold up to 2n2 electrons, this is the principle of Pauli incompatibility. The K layer is the shell with the lowest energy level, followed by the L layer, M layer, etc. The size of the energy level is equal to the electron binding energy of the shell. Under normal conditioons, high-energy electrons fill the low-energy levels, leaving the atoms in a stable state, when receiving X-rays, high energy particle beam irradiation. Because high-energy particles and photons collide with the sample atoms, the inner electrons of the atoms are expelled, and form holes in its place, so the atoms are in an excited state. This kind of ion in the excited state has a very short life. When the outer layer electrons transition to the inner layer holes, the excess energy will be released in the form of X-rays. It creates new holes

And new X-ray emissions in the outer layer, thereby producing a series of characteristic X-rays. If you want to get the characteristic X-rays of an element, you need to excite the inner electrons of the element atoms, so that inner electrons get a certain amount of energy, which can get rid of the nucleus, and form electron holes in the inner orbit. When higher-level electrons fill this hole, characteristic X-rays of a certain energy are emitted. This process is the excitation of X-rays, which is the basic principle of X-ray fluorescence.



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